The present invention relates to a method and a device for controlling the braking torque of a brake force regulator at at least one wheel of a motor vehicle.
A method for determining the braking force at a wheel of a vehicle is described in German Patent No. 39 23 599 in which the wheel speed and the brake pressure are measured. A new parameter for the braking force at the wheel is determined from these measured quantities with the aid of a parameter estimation method.
In the case of the brake-slip controller according to German Published Patent Application No. 37 31 075, the difference between a permissible brake slip and the actual brake slip is determined. Control times for a control unit which regulates the brake pressure are determined from this difference by a control amplifier. The control is temporarily interrupted for short periods and recalculated subsequent to updating the measured parameters. In this context, it has turned out that in the calculation of the control times for the pressure valve, no consideration was made as to whether the hydraulic pump is still in operation or completely at rest subsequent to switching off the control signal. Since, when the hydraulic pump is still in operation, an increased initial pressure is present in the line system and affects the control times for the valve.
The method and the device according to the present invention for controlling the brake torque of a brake force regulator has the advantage over the background art that the control times for the valve of a wheel brake cylinder can be calculated as a function of the actual pressure which is present in the line prior to the beginning of the control. It is particularly advantageous that the standstill of the electric motor of the hydraulic pump can be detected by a simple measurement of the induced voltage.
It is particularly advantageous that the pressure in the line is measured without any additional sensor via the coasting of the hydraulic pump subsequent to switching off the control signal. This is advantageously carried out by measuring the induced voltage (e.m.f.) at the field winding of the pump motor.
In this context, to determine the standstill of the hydraulic pump, it is advantageously assumed that the pressure in the hydraulic system has largely dropped when the measured voltage lies below a predefined limit value. In this manner, the waiting times until the standstill of the hydraulic pump are prevented from becoming excessively long. In this manner, one also succeeds in increasing the brake pressure in the system in a pulsed manner without all too long time intervals. This advantageously results in that the wheel is braked with a controlled slip, thus attaining optimum deceleration values of the vehicle.